1. Technical Field
The present application relates generally to a gas sensor control apparatus designed to change an output characteristic such as a response time of a gas sensor as needed.
2. Background Art
Gas sensors are known which measure the concentration of oxygen contained in exhaust gas from an automotive engine as representing an air-fuel ratio of a mixture supplied to the engine. For example, typical electromotive force O2 sensors work to output an electric signal which is different in level between when the exhaust gas is rich in fuel and when the exhaust gas is lean in fuel. Specifically, such a type of O2 sensors produces about 0.9V when an air-fuel ratio of the exhaust gas is in a rich state and about 0V when the air-fuel ratio is in a lean state.
The typical gas sensors usually experience a time lag in reacting to an actual change in air-fuel ratio of the exhaust gas to produce the output. The improvement of the time lag has been sought.
For example, Japanese Patent Second Publication No. 8-20414 discloses the electromotive force O2 sensor equipped with an auxiliary electrochemical cell. The auxiliary electrochemical cell is connected to one of electrodes of the O2 sensor. The electric current is applied to the auxiliary electrochemical cell to perform the so-called ion pumping, thereby changing the concentration of gas to be measured, that is, a λ characteristic (i.e., an electromotive force characteristic) in relation to the applied current.
The production of the electromotive force O2 sensor of the above publication requires modifying the structure of a typical O2 sensor greatly, thus resulting in an increase in production cost thereof.